usb: Add driver for Altus Metrum ChaosKey device (v2)

This is a hardware random number generator. The driver provides both a
/dev/chaoskeyX entry and hooks the entropy source up to the kernel
hwrng interface. More information about the device can be found at
http://chaoskey.org

The USB ID for ChaosKey was allocated from the OpenMoko USB vendor
space and is visible as 'USBtrng' here:

http://wiki.openmoko.org/wiki/USB_Product_IDs

v2: Respond to review from Oliver Neukum <oneukum@suse.de>

 * Delete extensive debug infrastructure and replace it with calls to
   dev_dbg.

 * Allocate I/O buffer separately from device structure to obey
   requirements for non-coherant architectures.

 * Initialize mutexes before registering device to ensure that open
   cannot be invoked before the device is ready to proceed.

 * Return number of bytes read instead of -EINTR when partial read
   operation is aborted due to a signal.

 * Make sure device mutex is unlocked in read error paths.

 * Add MAINTAINERS entry for the driver

Signed-off-by: Keith Packard <keithp@keithp.com>
Cc: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 543 insertions, 0 deletions

diff --git a/drivers/usb/misc/Kconfig b/drivers/usb/misc/Kconfig
index 76d77206e011..8c331f1dfd23 100644
--- a/drivers/usb/misc/Kconfig
+++ b/drivers/usb/misc/Kconfig
@@ -255,3 +255,15 @@ config USB_LINK_LAYER_TEST
           This driver is for generating specific traffic for Super Speed Link
           Layer Test Device. Say Y only when you want to conduct USB Super Speed
           Link Layer Test for host controllers.
+
+config USB_CHAOSKEY
+        tristate "ChaosKey random number generator driver support"
+        help
+          Say Y here if you want to connect an AltusMetrum ChaosKey to
+          your computer's USB port. The ChaosKey is a hardware random
+          number generator which hooks into the kernel entropy pool to
+          ensure a large supply of entropy for /dev/random and
+          /dev/urandom and also provides direct access via /dev/chaoskeyX
+
+          To compile this driver as a module, choose M here: the
+          module will be called chaoskey.
diff --git a/drivers/usb/misc/Makefile b/drivers/usb/misc/Makefile
index 65b0402c1ca1..45fd4ac39d3e 100644
--- a/drivers/usb/misc/Makefile
+++ b/drivers/usb/misc/Makefile
@@ -25,6 +25,7 @@ obj-$(CONFIG_USB_USS720)		+= uss720.o
 obj-$(CONFIG_USB_SEVSEG)                += usbsevseg.o
 obj-$(CONFIG_USB_YUREX)                 += yurex.o
 obj-$(CONFIG_USB_HSIC_USB3503)          += usb3503.o
+obj-$(CONFIG_USB_CHAOSKEY)              += chaoskey.o
 
 obj-$(CONFIG_USB_SISUSBVGA)             += sisusbvga/
 obj-$(CONFIG_USB_LINK_LAYER_TEST)       += lvstest.o
diff --git a/drivers/usb/misc/chaoskey.c b/drivers/usb/misc/chaoskey.c
new file mode 100644
index 000000000000..ef80ce9452a4
--- /dev/null
+++ b/drivers/usb/misc/chaoskey.c
@@ -0,0 +1,530 @@
+/*
+ * chaoskey - driver for ChaosKey device from Altus Metrum.
+ *
+ * This device provides true random numbers using a noise source based
+ * on a reverse-biased p-n junction in avalanche breakdown. More
+ * details can be found at http://chaoskey.org
+ *
+ * The driver connects to the kernel hardware RNG interface to provide
+ * entropy for /dev/random and other kernel activities. It also offers
+ * a separate /dev/ entry to allow for direct access to the random
+ * bit stream.
+ *
+ * Copyright © 2015 Keith Packard <keithp@keithp.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/usb.h>
+#include <linux/wait.h>
+#include <linux/hw_random.h>
+
+static struct usb_driver chaoskey_driver;
+static struct usb_class_driver chaoskey_class;
+static int chaoskey_rng_read(struct hwrng *rng, void *data,
+                             size_t max, bool wait);
+
+#define usb_dbg(usb_if, format, arg...) \
+        dev_dbg(&(usb_if)->dev, format, ## arg)
+
+#define usb_err(usb_if, format, arg...) \
+        dev_err(&(usb_if)->dev, format, ## arg)
+
+/* Version Information */
+#define DRIVER_VERSION  "v0.1"
+#define DRIVER_AUTHOR   "Keith Packard, keithp@keithp.com"
+#define DRIVER_DESC     "Altus Metrum ChaosKey driver"
+#define DRIVER_SHORT    "chaoskey"
+
+MODULE_VERSION(DRIVER_VERSION);
+MODULE_AUTHOR(DRIVER_AUTHOR);
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+#define CHAOSKEY_VENDOR_ID      0x1d50  /* OpenMoko */
+#define CHAOSKEY_PRODUCT_ID     0x60c6  /* ChaosKey */
+
+#define CHAOSKEY_BUF_LEN        64      /* max size of USB full speed packet */
+
+#define NAK_TIMEOUT (HZ)                /* stall/wait timeout for device */
+
+#ifdef CONFIG_USB_DYNAMIC_MINORS
+#define USB_CHAOSKEY_MINOR_BASE 0
+#else
+
+/* IOWARRIOR_MINOR_BASE + 16, not official yet */
+#define USB_CHAOSKEY_MINOR_BASE 224
+#endif
+
+static const struct usb_device_id chaoskey_table[] = {
+        { USB_DEVICE(CHAOSKEY_VENDOR_ID, CHAOSKEY_PRODUCT_ID) },
+        { },
+};
+MODULE_DEVICE_TABLE(usb, chaoskey_table);
+
+/* Driver-local specific stuff */
+struct chaoskey {
+        struct usb_interface *interface;
+        char in_ep;
+        struct mutex lock;
+        struct mutex rng_lock;
+        int open;                       /* open count */
+        int present;                    /* device not disconnected */
+        int size;                       /* size of buf */
+        int valid;                      /* bytes of buf read */
+        int used;                       /* bytes of buf consumed */
+        char *name;                     /* product + serial */
+        struct hwrng hwrng;             /* Embedded struct for hwrng */
+        int hwrng_registered;           /* registered with hwrng API */
+        wait_queue_head_t wait_q;       /* for timeouts */
+        char *buf;
+};
+
+static void chaoskey_free(struct chaoskey *dev)
+{
+        usb_dbg(dev->interface, "free");
+        kfree(dev->name);
+        kfree(dev->buf);
+        kfree(dev);
+}
+
+static int chaoskey_probe(struct usb_interface *interface,
+                          const struct usb_device_id *id)
+{
+        struct usb_device *udev = interface_to_usbdev(interface);
+        struct usb_host_interface *altsetting = interface->cur_altsetting;
+        int i;
+        int in_ep = -1;
+        struct chaoskey *dev;
+        int result;
+        int size;
+
+        usb_dbg(interface, "probe %s-%s", udev->product, udev->serial);
+
+        /* Find the first bulk IN endpoint and its packet size */
+        for (i = 0; i < altsetting->desc.bNumEndpoints; i++) {
+                if (usb_endpoint_is_bulk_in(&altsetting->endpoint[i].desc)) {
+                        in_ep = altsetting->endpoint[i].desc.bEndpointAddress;
+                        size = altsetting->endpoint[i].desc.wMaxPacketSize;
+                        break;
+                }
+        }
+
+        /* Validate endpoint and size */
+        if (in_ep == -1) {
+                usb_dbg(interface, "no IN endpoint found");
+                return -ENODEV;
+        }
+        if (size <= 0) {
+                usb_dbg(interface, "invalid size (%d)", size);
+                return -ENODEV;
+        }
+
+        if (size > CHAOSKEY_BUF_LEN) {
+                usb_dbg(interface, "size reduced from %d to %d\n",
+                        size, CHAOSKEY_BUF_LEN);
+                size = CHAOSKEY_BUF_LEN;
+        }
+
+        /* Looks good, allocate and initialize */
+
+        dev = kzalloc(sizeof(struct chaoskey), GFP_KERNEL);
+
+        if (dev == NULL)
+                return -ENOMEM;
+
+        dev->buf = kmalloc(size, GFP_KERNEL);
+
+        if (dev->buf == NULL) {
+                kfree(dev);
+                return -ENOMEM;
+        }
+
+        /* Construct a name using the product and serial values. Each
+         * device needs a unique name for the hwrng code
+         */
+
+        if (udev->product && udev->serial) {
+                dev->name = kmalloc(strlen(udev->product) + 1 +
+                                    strlen(udev->serial) + 1, GFP_KERNEL);
+                if (dev->name == NULL) {
+                        kfree(dev->buf);
+                        kfree(dev);
+                        return -ENOMEM;
+                }
+
+                strcpy(dev->name, udev->product);
+                strcat(dev->name, "-");
+                strcat(dev->name, udev->serial);
+        }
+
+        dev->interface = interface;
+
+        dev->in_ep = in_ep;
+
+        dev->size = size;
+        dev->present = 1;
+
+        init_waitqueue_head(&dev->wait_q);
+
+        mutex_init(&dev->lock);
+        mutex_init(&dev->rng_lock);
+
+        usb_set_intfdata(interface, dev);
+
+        result = usb_register_dev(interface, &chaoskey_class);
+        if (result) {
+                usb_err(interface, "Unable to allocate minor number.");
+                usb_set_intfdata(interface, NULL);
+                chaoskey_free(dev);
+                return result;
+        }
+
+        dev->hwrng.name = dev->name ? dev->name : chaoskey_driver.name;
+        dev->hwrng.read = chaoskey_rng_read;
+
+        /* Set the 'quality' metric.  Quality is measured in units of
+         * 1/1024's of a bit ("mills"). This should be set to 1024,
+         * but there is a bug in the hwrng core which masks it with
+         * 1023.
+         *
+         * The patch that has been merged to the crypto development
+         * tree for that bug limits the value to 1024 at most, so by
+         * setting this to 1024 + 1023, we get 1023 before the fix is
+         * merged and 1024 afterwards. We'll patch this driver once
+         * both bits of code are in the same tree.
+         */
+        dev->hwrng.quality = 1024 + 1023;
+
+        dev->hwrng_registered = (hwrng_register(&dev->hwrng) == 0);
+        if (!dev->hwrng_registered)
+                usb_err(interface, "Unable to register with hwrng");
+
+        usb_enable_autosuspend(udev);
+
+        usb_dbg(interface, "chaoskey probe success, size %d", dev->size);
+        return 0;
+}
+
+static void chaoskey_disconnect(struct usb_interface *interface)
+{
+        struct chaoskey *dev;
+
+        usb_dbg(interface, "disconnect");
+        dev = usb_get_intfdata(interface);
+        if (!dev) {
+                usb_dbg(interface, "disconnect failed - no dev");
+                return;
+        }
+
+        if (dev->hwrng_registered)
+                hwrng_unregister(&dev->hwrng);
+
+        usb_deregister_dev(interface, &chaoskey_class);
+
+        usb_set_intfdata(interface, NULL);
+        mutex_lock(&dev->lock);
+
+        dev->present = 0;
+
+        if (!dev->open) {
+                mutex_unlock(&dev->lock);
+                chaoskey_free(dev);
+        } else
+                mutex_unlock(&dev->lock);
+
+        usb_dbg(interface, "disconnect done");
+}
+
+static int chaoskey_open(struct inode *inode, struct file *file)
+{
+        struct chaoskey *dev;
+        struct usb_interface *interface;
+
+        /* get the interface from minor number and driver information */
+        interface = usb_find_interface(&chaoskey_driver, iminor(inode));
+        if (!interface)
+                return -ENODEV;
+
+        usb_dbg(interface, "open");
+
+        dev = usb_get_intfdata(interface);
+        if (!dev) {
+                usb_dbg(interface, "open (dev)");
+                return -ENODEV;
+        }
+
+        file->private_data = dev;
+        mutex_lock(&dev->lock);
+        ++dev->open;
+        mutex_unlock(&dev->lock);
+
+        usb_dbg(interface, "open success");
+        return 0;
+}
+
+static int chaoskey_release(struct inode *inode, struct file *file)
+{
+        struct chaoskey *dev = file->private_data;
+        struct usb_interface *interface;
+
+        if (dev == NULL)
+                return -ENODEV;
+
+        interface = dev->interface;
+
+        usb_dbg(interface, "release");
+
+        mutex_lock(&dev->lock);
+
+        usb_dbg(interface, "open count at release is %d", dev->open);
+
+        if (dev->open <= 0) {
+                usb_dbg(interface, "invalid open count (%d)", dev->open);
+                mutex_unlock(&dev->lock);
+                return -ENODEV;
+        }
+
+        --dev->open;
+
+        if (!dev->present) {
+                if (dev->open == 0) {
+                        mutex_unlock(&dev->lock);
+                        chaoskey_free(dev);
+                } else
+                        mutex_unlock(&dev->lock);
+        } else
+                mutex_unlock(&dev->lock);
+
+        usb_dbg(interface, "release success");
+        return 0;
+}
+
+/* Fill the buffer. Called with dev->lock held
+ */
+static int _chaoskey_fill(struct chaoskey *dev)
+{
+        DEFINE_WAIT(wait);
+        int result;
+        int this_read;
+        struct usb_device *udev = interface_to_usbdev(dev->interface);
+
+        usb_dbg(dev->interface, "fill");
+
+        /* Return immediately if someone called before the buffer was
+         * empty */
+        if (dev->valid != dev->used) {
+                usb_dbg(dev->interface, "not empty yet (valid %d used %d)",
+                        dev->valid, dev->used);
+                return 0;
+        }
+
+        /* Bail if the device has been removed */
+        if (!dev->present) {
+                usb_dbg(dev->interface, "device not present");
+                return -ENODEV;
+        }
+
+        /* Make sure the device is awake */
+        result = usb_autopm_get_interface(dev->interface);
+        if (result) {
+                usb_dbg(dev->interface, "wakeup failed (result %d)", result);
+                return result;
+        }
+
+        result = usb_bulk_msg(udev,
+                              usb_rcvbulkpipe(udev, dev->in_ep),
+                              dev->buf, dev->size, &this_read,
+                              NAK_TIMEOUT);
+
+        /* Let the device go back to sleep eventually */
+        usb_autopm_put_interface(dev->interface);
+
+        if (result == 0) {
+                dev->valid = this_read;
+                dev->used = 0;
+        }
+
+        usb_dbg(dev->interface, "bulk_msg result %d this_read %d",
+                result, this_read);
+
+        return result;
+}
+
+static ssize_t chaoskey_read(struct file *file,
+                             char __user *buffer,
+                             size_t count,
+                             loff_t *ppos)
+{
+        struct chaoskey *dev;
+        ssize_t read_count = 0;
+        int this_time;
+        int result = 0;
+        unsigned long remain;
+
+        dev = file->private_data;
+
+        if (dev == NULL || !dev->present)
+                return -ENODEV;
+
+        usb_dbg(dev->interface, "read %zu", count);
+
+        while (count > 0) {
+
+                /* Grab the rng_lock briefly to ensure that the hwrng interface
+                 * gets priority over other user access
+                 */
+                result = mutex_lock_interruptible(&dev->rng_lock);
+                if (result)
+                        goto bail;
+                mutex_unlock(&dev->rng_lock);
+
+                result = mutex_lock_interruptible(&dev->lock);
+                if (result)
+                        goto bail;
+                if (dev->valid == dev->used) {
+                        result = _chaoskey_fill(dev);
+                        if (result) {
+                                mutex_unlock(&dev->lock);
+                                goto bail;
+                        }
+
+                        /* Read returned zero bytes */
+                        if (dev->used == dev->valid) {
+                                mutex_unlock(&dev->lock);
+                                goto bail;
+                        }
+                }
+
+                this_time = dev->valid - dev->used;
+                if (this_time > count)
+                        this_time = count;
+
+                remain = copy_to_user(buffer, dev->buf + dev->used, this_time);
+                if (remain) {
+                        result = -EFAULT;
+
+                        /* Consume the bytes that were copied so we don't leak
+                         * data to user space
+                         */
+                        dev->used += this_time - remain;
+                        mutex_unlock(&dev->lock);
+                        goto bail;
+                }
+
+                count -= this_time;
+                read_count += this_time;
+                buffer += this_time;
+                dev->used += this_time;
+                mutex_unlock(&dev->lock);
+        }
+bail:
+        if (read_count) {
+                usb_dbg(dev->interface, "read %zu bytes", read_count);
+                return read_count;
+        }
+        usb_dbg(dev->interface, "empty read, result %d", result);
+        return result;
+}
+
+static int chaoskey_rng_read(struct hwrng *rng, void *data,
+                             size_t max, bool wait)
+{
+        struct chaoskey *dev = container_of(rng, struct chaoskey, hwrng);
+        int this_time;
+
+        usb_dbg(dev->interface, "rng_read max %zu wait %d", max, wait);
+
+        if (!dev->present) {
+                usb_dbg(dev->interface, "device not present");
+                return 0;
+        }
+
+        /* Hold the rng_lock until we acquire the device lock so that
+         * this operation gets priority over other user access to the
+         * device
+         */
+        mutex_lock(&dev->rng_lock);
+
+        mutex_lock(&dev->lock);
+
+        mutex_unlock(&dev->rng_lock);
+
+        /* Try to fill the buffer if empty. It doesn't actually matter
+         * if _chaoskey_fill works; we'll just return zero bytes as
+         * the buffer will still be empty
+         */
+        if (dev->valid == dev->used)
+                (void) _chaoskey_fill(dev);
+
+        this_time = dev->valid - dev->used;
+        if (this_time > max)
+                this_time = max;
+
+        memcpy(data, dev->buf, this_time);
+
+        dev->used += this_time;
+
+        mutex_unlock(&dev->lock);
+
+        usb_dbg(dev->interface, "rng_read this_time %d\n", this_time);
+        return this_time;
+}
+
+#ifdef CONFIG_PM
+static int chaoskey_suspend(struct usb_interface *interface,
+                            pm_message_t message)
+{
+        usb_dbg(interface, "suspend");
+        return 0;
+}
+
+static int chaoskey_resume(struct usb_interface *interface)
+{
+        usb_dbg(interface, "resume");
+        return 0;
+}
+#else
+#define chaoskey_suspend NULL
+#define chaoskey_resume NULL
+#endif
+
+/* file operation pointers */
+static const struct file_operations chaoskey_fops = {
+        .owner = THIS_MODULE,
+        .read = chaoskey_read,
+        .open = chaoskey_open,
+        .release = chaoskey_release,
+        .llseek = default_llseek,
+};
+
+/* class driver information */
+static struct usb_class_driver chaoskey_class = {
+        .name = "chaoskey%d",
+        .fops = &chaoskey_fops,
+        .minor_base = USB_CHAOSKEY_MINOR_BASE,
+};
+
+/* usb specific object needed to register this driver with the usb subsystem */
+static struct usb_driver chaoskey_driver = {
+        .name = DRIVER_SHORT,
+        .probe = chaoskey_probe,
+        .disconnect = chaoskey_disconnect,
+        .suspend = chaoskey_suspend,
+        .resume = chaoskey_resume,
+        .reset_resume = chaoskey_resume,
+        .id_table = chaoskey_table,
+        .supports_autosuspend = 1,
+};
+
+module_usb_driver(chaoskey_driver);
+